Chapter 7 - Energy Metabolism

Acetyl CoA

(A 2-carbon structure with coenzyme A attached; cannot be used to make glucose) - Fatty acids are converted to acetyl CoA (therefore cannot make glucose) - Acetyl CoA enters TCA cycle and energy harnessed through electon transport chain

Electron transport chain

(a.k.a respiratory chain) - The final pathway in energy metabolism that transports electrons from hydrogen to oxygen and captures the energy released in the bonds of ATP

Pyruvate

(A 3-carbon structure; can be used to make glucose) - Amino acids and glycerol converted to pyruvate (therefore can make glucose)

TCA cycle

(a.k.a citric acid cycle or krebs cycle) - Series of metabolic reactions that breaks down molecules of acetyl CoA to carbon dioxide and hydrogen atoms

During the first few days of a fast, body protein provides about what percentage of the glucose the body needs to fuel itself?

90%

What is acetaldehyde?

A toxic compound created in alcohol metabolism

Which of the following is a feature of aerobic metabolism?

Energy is produced more slowly than in anaerobic metabolism

___ is the preferred form of energy storage

Fat

The kCalorie-Per-Gram Secret Revealed

Fat provides most energy per gram - More carbon-hydrogen bonds to which oxygen can be added - hydrogens released, go to ETC More ATP=more kcalories - One glucose molecule = 30-32 ATP - One 16 carbon fatty acid = 129 ATP

What is the reason that fat yields more calories than carbohydrate or protein?

Fats contains many carbon-hydrogen bond that can be readily oxidized.

Amino acids that enter the TCA cycle directly are considered _________

Glucogenic

In energy metabolism, glycerol can convert to ________

Glucose or pyruvate

For short, intense exercise, which energy producing pathway does the body rely on most?

Glucose to pyruvate to lactate

Transition from feasting to fasting

Glucose, glycerol, and fatty acids are used as needed then stores - As body shifts to fasted state, uses the stored Energy is always needed When fasting/starving, body draws upon reserves - Protein tissues after one day - Then cells degrade their own components for fuel

All life initially comes from photosynthesis

Green plants use the sun's energy to make carbohydrates. Humans eat the plants, or eat the animals that eat the plants.

4 Types of energy

Heat, mechanical, electrical, and chemical

Energy metabolism

How the body obtains and uses foods to meet its needs - Releases energy, water, carbon dioxide (and other waste)

When the body needs energy quickly, pyruvate is converted to ________

Lactate

In the cori cycle, lactate is converted to glucose in the _________

Liver

What is the major site for gluconeogenesis?

Liver

Which cells are the most metabolically active and most versatile

Liver cells

Liver cells are the most metabolically active and versatile

Liver cells are the most metabolically active and versatile

When health experts say to consume alcohol in moderation what do they mean/

Men should have no more than two drinks per day; women, no more than one drink per day.

Excess fat

Most direct and efficient conversion (disassembles TGs, absorbs parts, reassembles in adipose)

Fatty acids can/cannot make glucose

Cannot

The process of making glucose from non carbohydrate sources is called

Gluconeogenesis

the metabolic breakdown of glucose to pyruvate is known as

Glycolysis

Which statement defines a coenzyme?

An organic molecule closely associated with enzymes

Acetyl CoA is the building block of ____

Fat

Which of these statements about the electron transport chain is true?

It captures energy in the ATP bonds

Examples of catabolic reactions

The breakdown of - glycogen - triglycerides - protein

Too much fat and inadequate CHO =

body needs to break down protein tissue to make glucose

What are the "powerhouses" of the cell?

mitochondria

The process of converting lactate from muscles to glucose in the liver that can be returned to the muscles is known as ________

the cori cycle

How soon would death occur from starvation if the body was unable to shift to a state of ketosis?

within 3 weeks

Pyruvate - to - Acetyl CoA

- 3-carbon Pyruvate enters mitochondria -- C00H carbon group removed --- becomes carbon dioxide -- 2-carbon compound joins with CoA, yields acetyl CoA --- irreversible - can't retrieve carbon from carbon dioxide - Acetyl CoA pathways discussed later

Fatty acids-to-acetyl CoA

- Fatty acid oxidation (or beta-oxidation) breaks down FAs 2 carbons at a time; each fragment combines with a moelcule of CoA to create acetyl CoA -- Hydrogens and electrons released and carried to ETC by conenzymes made from riboflavin and niacin

Excess carbohydrate

- First stored as glycogen - Glucose absorbed, dismantled to pyruvate and acetyl CoA, many acetyl CoA's assembled into fatty acid and attached to glycerol

Glucose - to - Pyruvate

- Glucose central to all cells' metabolism; liver can convert fructose and galactose to glucose - Glycolysis - Pyruvate can be converted back to glucose -- Liver cells and (to some extent) kidneys

Glycerol-to-pyruvate

- Glycerol (3 carbons) can be converted to another 3-carbon compound that can go "up" to glucose or "down" to pyruvate

Adaptation: conserving energy

- Hormones of fasting slow metabolism - As lean protein tissues diminish, less metabolic work is done (less energy demanded) - Weight loss, not necessarily fat loss - Adaptation to help sustain life for up to 2 months

Catabolic reactions

- Large molecules are broken down into smaller ones - Release energy

Alcohol in the liver

- Liver cells are the first to receive alcohol-laden blood - Alcohol dehydrogenase - Disrupts liver activity - fatty acids accumulate while alcohol is being metabolized - Can permanently change liver cell structure, impairing ability to metabolize fats -- fatty liver

Adaptation: making glucose

- Most cells can use fatty acids; RBCs and CNS need glucose - Amino acids that yield pyruvate can be used for gluconeogenesis (mainly happens in the liver, but kidneys become involved in starvation) - To get amino acids, muscle and liver break down to some extent during fasting

Adverse side affects of low carb, ketogenic diets

- Nausea - Fatigue (especially if physically active - Constipation - Low blood pressure - Elevated uric acid (which may exacerbate kidney disease and cause inflammation of the joints in those predisposed to gout) - Stale, foul taste in the mouth (bad breath) - In pregnant women, fetal harm and stillbirth

Alcohol in the body

- Potential health benefits for older adults - Lipid solvent -- Out of cell membranes, can lead to cell death - Moderation - alcohol is a drug -- Tolerance is highly individual -- Max. of one drink/day for females, two drinks/day for males

Glycolysis

- 2 Pyruvate molecules - Hydrogen atoms and electrons carried to electron transport chain (using coenzymes) - Requires 2 ATP to begin process; yields 4 ATP total; with net yield of 2 ATP.

Pyruvate - to - Lactate

- Pyruvate accepts hydrogens (if ETC is unable to accept them - lack of mitochondria, insufficient oxygen) --- Converts pyruvate to lactate - Occurs to a limited extent at rest, but mainly during high-intensity excercise - Produces ATP quickly - Only sustainable for a coouple of minutes - Lactate accumulation in muscles --- Coincides with but does not cause drop in blood pH, muscle pain, and fatigue - Cori cycle - Lactate to glucose in the liver

Low carbohydrate diets

- Similar effects to fasting: body uses glycogen then makes glucose. Even with high protein diets, body proteins catabolized - Increased urine production when glycogen and protein broken down - Ketosis occurs (ketones detected in urine) -- No relation btwn ketosis and long-term weight loss -- Initial weight loss often gained back when return to normal diet - Effectively used in treatment of epilepsy

Anabolic reactions

- Small molecules put together to build larger ones - Require input of energy

Intermittent fasting

- Some alternate days of no energy consumption with days of eating anything; some modify - Usually results ins imilar weight loss to energy-restricted weight loss plans; may be some additional health benefits - Time restricted-feeding-- defines a set time frame for eating -- May improve body weight, blood lipids, and blood glucose

Rate of alcohol metabolism

- acetaldehyde - highly reactive and toxic - Acetate - converted to carbon dioxide or acetyl CoA -- Hydrogens produced, go to ETC with help of niacin -- takes niacin away from other important metabolic reactions

Feasting - Excess energy

-Metabolism favors fat formation --Regardless of excess from protein, fat, or carbohydrates -Fuel mix

Adaptation: creating an Alternative fuel

1. Acetyl CoA fragments are combined to produce ketone bodies - Keto acid - ketone body that contains an acid group (-COOH) - When accumulation rises, pH of blood drops - ketosis - Acidic blood denatures protein - Fruity odor on breath develops - Induces a loss of appetite 2. Parts of brain rely exclusively on glucose, so body continues to sacrifice protein at a slower rate

Alcohols influence in the brain

1. Alcohol is a narcotic 2. Sedates inhibitory neveres - Central nervous system depressant 3. Blood alcohol levels and brain respones 4. Brain and liver cell death - Liver cells regenerate; some brain cells do not 5. Depression of antidiuretic hormone (ADH) - Loss of body water, leads to thirst and often consuming more alcohol - Loss of important minerals

Breaking down amino acids

1. Amino acids must first be deaminated 2. Many different ways amino can enter energy pathways - Most can be converted to pyruvate (can provide glucose) --- Glucogenic - Some converted to acetyl CoA (provides additional energy or body fat but can't make glucose) -- Ketogenic - Some enter TCA cycle directly as compounds other than acetyl CoA (can generate energy or glucose)

Alcohols effect on weight

1. Contributes to body fat and weight gain - Central obesity (beer belly) One ounce of alcohol represents 0.5 ounce of fat 2. Alcohol often replaces a meal - Malnutrition - 7 kcalories per gram 3. Nutrient displacement - B vitamins - Chronic alcoholism wernicke-kosakoff syndrome

Helpers in metabolic reactions

1. Enzymes - Facilitators of metabolic reactions - Proteins 2. Co-enzymes - Organic - Associate with enzymes - Without coenzyme, an enzyme cannot function

TCA Cycle

1. Final common metabolic pathway for CHO, fats, and amino acids - acetyl CoA enters 2. Takes place in inner compartment of mitochondria 3. Oxaloacetate is needed in first stem, and synthesized in last step - TCA slows when oxaloacetate is insufficient - Made primarily from pyruvate, some amino acids (not fat) - Oxaloacetate combines with acetyl CoA to become 6 carbon compound, then releases carbons as carbon dioxide. 4. Hydrogen atoms carried by conenzymes made from B vitamins (niacin and riboflavin) to the ETC

Oce acetyl CoA is formed, it has two main options:

1. Generate ATP 2. Make fats

Electron transport chain

1. The electron transport chain captures energy in the high-energy bonds of ATP - Occurs on inner membrane of mitrochondria - A series of proteins that serves as electron "carriers" - Electrons passed down until they reach oxygen, which accepts electron and combines with hydrogen to form water (this is why oxygen is essential to life) - As electrons are passed down, hydrogens pumped across membrane to outer compartment of mitochondria -- the flow of hydrogen back into inner compartment is what powers synthesis of ATP -- ATP leaves mitochondria and enters cytoplasm where it is used for energy

Final steps of energy metabolism

1. To make glucose: - All CHO - Most amino acids - Glycerol portion of triglycerides 2. To make (nonessential) proteins: - Glucose or glycerol, when nitrogen is available 3. To make fats: - Excess of all of the nutrients (acetyl CoA) 4. Acetyl CoA has to main fates: - Synthesis fats; or - generate ATP

Some of the energy released during the breakdown of glucose, glycerol, fatty acids, and amino acids is captured in the high energy compound with three phosphate groups called ____.

ATP

Which metabolic reaction occurs when a cell releases energy?

ATP releases a phosphate group and becomes ADP

Which of the following is a feature of ketosis?

Acetone breath fruity breath

Fatty acid oxidation produces _____________

Acetyl CoA

Which of the following compounds can be synthesized by carbohydrate, protein, and fat?

Acetyl CoA

Transfer of energy in reactions - ATP

Adenosine triphosphate (ATP): High energy compound composed of a purine (adenine), a sugar (ribose), and three phosphate groups - Hydrolysis of bonds between phosphate groups releases energy.. often occurs simultaneously with reactions that will use the energy released (coupled reactions) - Body converts chemical energy of food to ATP with 50% efficiency (the rest is radiated as heat)

Alcohols influence

Alcohol is not digested- absorbed directly across the walls of an empty stomach and goes straight to brain within minutes - delayed with food in the stomach Broken down with alcohol dehydrogenase in stomach - Women produce less, so more alcohol goes into SI and is absorbed, compared to men of the same size Once absorbed, it is metabolized before most nutrients (ensures speedy disposal) - Cannot be stored

Chemical reactions in the body

All reactions take place within the cells

When the carbohydrate content of the diet is insufficient to meat the body's needs for glucose, which of these compounded can be converted to glucose?

Amino acids

Excess protein

Amino acids are not stored; deaminated and remaining carbons are converted to ketone bodies which are stored as fat

Which of the these is an anabolic reaction

Amino acids to protein

Breaking down nutrients for energy

Carbohydrates are broken down during digestion to: Glucose Fats (triglycerides) are broken down to: Glycerol and fatty acids Proteins are broken down into: amino acids

Signs of alcoholism (2)

Cravings: the person has strong urges to use alcohol. Impaired ability: the person's intoxication or withdrawal symptoms interfere with work, school, or home. Problems: the person continues drinking despite physical hazards or medical, legal, psychological, family, employment, or school problems caused or exacerbated by alcohol. These conditions suggest that a person may have an alcohol problem and might benefit from an abstinence program or professional help.

Alcohol effects on the liver

Niacin conenzyme cause changes to normal processes - Glycolysis - TCA cycle - acetyl CoA builds up and goes to FA synthesis - Electron transport chain - Side effects of these changes -- fat accumulates in the liver -- Even after one night of heavy drinking -- Fatty liver is initially reversible --- Over time → fibrosis → cirrhosis MEOS - enzyme system that metabolizes both alcohol and several drugs - high intake stimulates production and leads to more efficient metabolism of alcohol and tolerance - Alcohol takes priority, so drugs may build up - Once alcohol use is discontinued, MEOS metabolizes drugs more quickly so doses need to be monitered

In the TCA cycle, which compound is involved in both the first and the last step?

Oxaloacetate

Pyruvate's Options

Quick energy needs - anaerobic Pyruvate to lactate Slower energy needs - aerobic Pyruvate to acetyl CoA

Before entering the metabolic pathways, amino acids first face ________

Removal of their nitrogen-containing amino group

Examples of anabolic reactions

The making of - glycogen - triglycerides - protein

Which of the following statements is not true of pyruvate?

The pathway of pyruvate to acetyl CoA is reversible

Metabolism

The sum total of all chemical reactions that go on in living cells

With regards to energy metabolism, which of the following statements is true about fatty acids?

They cannot make glucose

One way that all the energy-yielding nutrients are alike is that _________

They share the same final metabolic pathway, the TCA cycle

Signs of alcoholism

Tolerance: the person needs higher and higher intakes of alcohol to achieve intoxication. Withdrawal: the person who stops drinking experiences anxiety, agitation, increased blood pressure, or seizures, or seeks alcohol to relieve these symptoms. Impaired control: the person intends to have 1 or 2 drinks, but has many more instead, or the person tries to control or quit drinking, but efforts are unsuccessful. Disinterest: the person neglects important social, family, job, or school activities because of drinking. Time: the person spends a great deal of time obtaining and drinking alcohol or recovering from excessive drinking.

What is one explanation for why women have generally lower tolerance for alcohol than in men?

Women produce less of the enzyme dehydrogenase

Lipids (fatty acids)

Yields energy? - YES Yields glucose? - NO Yields amino acids and body proteins? - NO Yields fat storage? - YES

Carbohydrates (glucose)

Yields energy? - YES Yields glucose? - YES Yields amino acids and body proteins? - Yes: when nitrogen is available, can yield nonessential amino acids Yields fat storage? - YES

Lipids (Glycerol)

Yields energy? - YES Yields glucose? - YES: When carbohydrate is unavailable Yields amino acids and body proteins? - YES - when nitrogen is available, can yield nonessential amino acids Yields fat storage? - YES

Proteins (amino acids)

Yields energy? - YES Yields glucose? - YES: when carbohydrate is unavailable Yields amino acids and body proteins? - YES Yields fat storage - YES

The process in which fatty acids are taken apart 2 carbons at a time is known as

fatty acid oxidation